This invention relates to a system for producing understeer characteristics in an articulated vehicle which normally has a neutral steer characteristic. Road vehicles, such as automobiles, are usually designed with understeer characteristics to obtain desirable high speed handling. As opposed to vehicles with understeer, vehicles having oversteer characteristics will normally tend to break-away at the rear wheels in a turn at their adhesion limit before a loss of adhesion occurs in the front wheels. It is advantageous, therefore, to design in a given amount of understeer. Understeer characteristics are usually built into such vehicles by means of appropriate suspension geometry design. However, because many off-road vehicles, such as articulated loaders utilized in the earthmoving industry, have no suspension system, there has traditional been no convenient way to improve high speed handling by synthesizing understeer characteristics.
The need for improving on the usal neutral steer propensity in such vehicles is demonstrated when such vehicles are driven at relatively high speed over relatively smooth surfaces from job site to job site. Whereas at moderate speeds the vehicles are easily controlled and adequately safe, if higher speeds were safely attainable, the vehicle would be more valuable in that it could move from job site to job site in less time.
There have been prior art attempts to address this problem. Examples of such attempts are found in U.S. Pat. Nos. 3,338,328 to Cataldo, which teaches the sensing of vehicle wheel speed and wheel turning angle; 3,380,547 to Granry; and 3,249,173 to Gordon.
None of such prior art patents, however, teaches the utilization of lateral acceleration as the sole input signal to a control means for producing understeer in a vehicle and none teaches the particular location of an acceleration sensing device in the vehicle so as to minimize the effects of roll or inclination in the vehicle. The prior art also fails to provide a system for producing understeer in an articulated vehicle regardless of whether such vehicle is equipped with follow-up or non-follow-up type steering.
The present invention provides these features and also produces a steering system which, at high speeds, appears to the operator to be of the follow-up type but which, at low speeds, exhibits non-follow-up characteristics. The transition between the two modes of operation is smooth and practically unnoticeable to the operator.